JPH0449129B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a personal computer having an analog circuit operated by the same power supply as the operating power supply supplied to a digital circuit.

[Technical background of the invention and its problems]

When a personal computer is equipped with an analog circuit that handles analog signals such as images or high-pitched voices, and this analog circuit is operated by the same power source as the digital circuit, the power supply from the digital circuit or switching regulator, etc. This causes a problem in that switching noise enters the analog circuit via the power supply line and disturbs the output image or sound. A specific conventional circuit example at this time is shown in Figure 1, and an example of its output signal is shown in Figure 2.
As shown in the figure. Figure 1 shows the configuration of an analog circuit (hereinafter referred to as composite circuit) that generates a monochrome composite signal to be supplied to a CRT monitor. This is a digital circuit section (hereinafter referred to as a processor section) that includes a processor, CPU, memory, etc. 11, 12, 13, and 14 are display system output signal lines of the processor section 10, and among these, 11, 12, and 13 are 8 gradation lines from white to black, corresponding to each color signal of R, G, and B. A signal line 14 outputs a 3-bit signal indicating horizontal H and vertical V synchronization signals. 2
0 is a composite circuit that generates a monochrome composite signal as shown in FIG. 2 based on the signals from each of the signal lines 11, 12, 13, and 14.
_R1 to _R8 are resistors, _Q1 is a drive transistor, and OUT is the output terminal of the monochrome composite signal. Reference numeral 30 denotes an operating power supply (Vcc;
5V), and 31 is a Vcc line for supplying operating power (Vcc).

In the circuit shown in FIG.
The TTL level logic signals output to the display system output signal lines 11, 12, 13, and 14 are synthesized by the resistors _R1 to _R6 of the composite circuit 20 and converted into analog signals, and then the transistor Q ₁
applied to the base of Transistor _Q1 constitutes an emitter follower circuit, and the voltage drop between the base and emitter is directly output to the output terminal OUT as the emitter output. The monochrome composite signal output from this output terminal OUT is obtained by a combination of logic "1" and "0" (3 bits) on signal output lines 11, 12, and 13, as shown in FIG. It consists of a signal Ci indicating eight gradations of brightness from white W to black B, and horizontal H and vertical V signals.

Here, when switching noise generated from the digital circuit in the processor section 10 or the switching circuit in the power supply section 30 is applied to the Vcc line 31, the switching noise passes through the resistor R ₅ and the transistor Q ₁ and continues as it is. Output end OUT
Output to. FIG. 3 shows an example of this case, where switching noise N is added to the Vcc line 31 when a neutral color signal is being output from the output terminal OUT. By sending the monochrome composite signal from the output terminal OUT shown in Figure 3 to the CRT monitor,
The noise N portion is displayed on the display screen as bright and dark dust on an intermediate color. Normally, the switching noise generated from the digital circuit in the processor section 10, the power supply circuit in the power supply section 30, etc. has a high frequency and is output continuously at a constant period. Switching noise may cause striped patterns or flickering,
This results in a very ugly display screen. This striped pattern
This is because switching noise having a frequency component close to that of the horizontal synchronizing signal occurs on the Vcc line 31.

Conventionally, when digital circuits and analog circuits in a personal computer are operated with the same power supply, switching noise enters the analog circuits and has a large adverse effect on the analog output.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and in a personal computer having an analog circuit for image, audio, etc., the switching noise caused by the switching noise when the analog circuit is operated with the same operating power supply as the digital circuit. To provide a personal computer which is capable of outputting stable high-quality images, sounds, etc. by reliably preventing leakage into circuits.

[Summary of the invention]

The present invention provides a personal computer that supplies the same power to both the digital circuit and the analog circuit, by inserting a filter into the power supply line of the analog circuit to remove switching noise generated from the digital circuit or the power supply section. This system reliably prevents damage to images, audio, etc. caused by the switching noise entering the analog circuit.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5. FIG. 4 is a circuit configuration diagram of an example of a monochrome composite signal generation circuit. In the figure, the same parts as those in FIG. In the figure, 40 is the resistor _R5 of the composite circuit 20 and the power supply section 30.
This is a low-pass filter (LPF) for removing switching noise made of an L/C circuit, which is inserted between the Vcc line 31 and the low-pass filter 40. through the resistor R ₅ of the composite circuit 20
supplied to

FIG. 5 is a diagram showing a signal waveform outputted from the output terminal OUT of the monochrome composite circuit 20 shown in FIG. 4 above.

Here, to explain the operation of one embodiment, the power supply section 3
The operating power (Vcc) outputted from 0 is supplied to the processor section 10 and also to the composite circuit 20. Furthermore, the composite circuit 20
The operating power (Vcc) supplied to the transistor Q1 is supplied to the resistor _R5 connected to the base of the transistor _Q1 via the low-pass filter 40. Processor section 1
Signal lines 11, 12, 13, 14 output from 0
Each signal above (TTL level “1”/“0”) is connected to a resistor R ₁ ~
The signals are synthesized by _R6 , converted into an analog signal, and applied to the base of the transistor _Q1 . At this time, the switching noise N generated from the digital circuit in the processor section 10 or the power supply section 30 is transferred onto the Vcc line 31 of the power supply section 30 as shown in FIG.
Since operating power (Vcc) is supplied to _R5 through the low-pass filter 40, the transistor
The logic values of the signal lines 11, 12, 13, and 14 are the same as those of the signal lines 11, 12, 13, and 14, with no high-frequency switching nozzle appearing on the voltage waveform applied to the _base of Q1, and switching noise removed by the low-pass filter 40. Only the analog quantity signal that follows the transistor
Supplied on the base of _Q1 . This allows the output end
As shown in FIG. 5, a monochrome composite signal containing no switching noise is output from OUT. Therefore, a clear image that is not disturbed by switching noise is displayed on the display screen of the CRT monitor. That is, the low-pass filter 40 removes switching noise having a frequency component close to the horizontal synchronizing signal, thereby preventing the occurrence of striped patterns, which was a drawback of the prior art.

Although the above-mentioned embodiment has been explained using a monochrome composite signal generation circuit as an example, the present invention is not limited to this, and may be applied to an analog circuit that handles an analog audio signal or an analog circuit that handles a color analog signal. It can also be easily realized in circuits, etc.

〔Effect of the invention〕

As described in detail above, according to the present invention, in a personal computer having an analog circuit for image/audio, etc., when the analog circuit is operated on the same operating power supply as the digital circuit, switching noise caused by the analog circuit is reduced. It is possible to output stable, high-quality images, high-pitched voices, etc. by reliably preventing the rotation of images.

[Brief explanation of the drawing]

Figure 1 is a circuit block diagram showing the conventional circuit configuration, Figure 2 is a diagram showing a monochrome composite signal, Figure 3 is a diagram showing the output signal waveform in the circuit configuration shown in Figure 1 above, and Figure 4 is a diagram showing the main circuit configuration. FIG. 5 is a circuit block diagram showing one embodiment of the invention, and is a diagram showing output signal waveforms in the above embodiment. 10...Digital circuit section (processor section),
11, 12, 13, 14...Signal line (display system output signal line), 20...Analog circuit (composite circuit), _R1 , _R2 ,..., _R8 ...Resistor, _Q1 ...Transistor, OUT ...Output end.

Claims (1)

[Claims] 1. A first processing means that executes predetermined digital processing and outputs digital display data and horizontal/vertical synchronization signals, and a second processing means that converts the digital display data output from the first processing means into analog display data. processing means, display means for displaying the analog display data converted by the second processing means based on the horizontal/vertical synchronization signal, and a power supply for operation from the power supply means for connecting the first processing means and the an operating power supply line that supplies the second processing means and the operating power supply line that is inserted between the second processing means and the operating power supply line and generates the operating power from the first processing means or the operating power supply; A personal computer comprising a filter circuit comprising at least a coil and a capacitor for removing switching noise having a frequency component close to a horizontal synchronization signal.